The present invention relates to binoculars with an automatic focusing mechanism in which each of right and left objectives is provided with a light admitting window close thereto and independent thereof. Light entering through each light admitting window is introduced to a focus detecting element module through a movable reflex structure or a fixed reflex structure and a lens having a long focal length or a non-focus or afocal optical system attachment.
In ordinary binoculars, it is troublesome to manually rotate an adjustment ring for oculars to thereby achieve the focusing of the binoculars. Moreover, this manual operation is not accurate. In order to overcome these problems, heretofore auto-focus binoculars have been proposed in which light reflected by a fixed reflex structure and a movable reflex structure is introduced into a focus detecting element module and the oculars are moved in accordance with control signals generated in the module to thereby automatically perform the focusing operation. However, in such binoculars, light entering through the objectives is divided into ocular light and focus detecting element module light. As a result, the intensity of the image viewed through the oculars is reduced and at the same time the light supplied to the focusing detecting element module is insufficient and hence a desired focusing accuracy cannot be obtained in low light situations.
With the intention of overcoming these difficulties, the present applicant has proposed, in U.S. Pat. No. 4,262,988 filed on Dec. 28, 1979, binoculars having an automatic focusing mechanism in which, in order to provide both a fixed reflex structure and a movable reflex structure with a sufficient amount of light, right and left object-distance metering windows are formed independent of right and left objectives, respectively. However, in such binoculars, light reflected by the fixed reflecting member and the movable reflecting member is directly introduced to the focus detecting element module. Since the field angle of the binoculars is rather narrow in comparison with that of a camera, light from most of the view field (70% or more) is introduced into the module resulting in incorrect focusing as a whole. Therefore, it is impossible to focus a desired object on the image plane. Namely, if a large object upon which it is not desired to focus is positioned in the same field as a relatively small object upon which focusing is desired to be carried out, most of the view field is occupied by the large object. Even if the desired object is positioned in the middle of the view field, it is difficult to achieve desirable focusing in such a condition.